Dual-fin helmet



FIG. 1 is a side view of a dual-fin helmet showing my new design;

FIG. 2 is a top view thereof;

FIG. 3 is a bottom view thereof;

FIG. 4 is a front view thereof; and,

FIG. 5 is a rear view thereof. 

The ornamental design for a dual-fin helmet, as shown and described. 